The present invention relates to the production of a cushion or stock material with a predetermined internal structure to achieve desired compression properties from otherwise firmer but compressible or elastomeric material. The invention is best illustrated in the difficult application of an orthopedic cushion such as a mattress.
To support a body orthopedicly, it is generally accepted that a "constant force" cushion should produce a minimal constant support force over as large an area of the body as possible with a corresponding minimum of additional force applied to broadly heavier regions (or protrusions) and lesser forces on lighter regions.
These conditions should result in a minimum of force applied where body regions are minimally sheered by differing amounts of support force and where necessary support force is applied to body concavities. The ideal cushion should achieve this without sagging over time or under excess weight and thus provide body alignment and a defined stop zone for the constant force motion.
Constant force cushions are, however, somewhat difficult to achieve in practice because common springs or foams produce increasing force with compression; and, even bladder structures such as air or water beds typically have surface effects from the bladder itself, rather than constant pressure within, which shift forces toward body protrusions and away from body concavities. Inflexibility or inelasticity of support surface layers can also prevent support forces from filly reaching body concavities such as the lower back. And, finally, mattress type constructions can suffer from "sag" over time or if improperly weighted or inflated.
In beds and other elastomer cushions, attempts to alter material properties have centered principally on foams, their microcell properties and elasticity with even the best foams having only slightly elongated force curves and generally heavier (hence more costly) formulations.
Various bed and cushion applications have employed cavities in foam or rubber materials but these generally suffer from increasing force curves, insufficient support efficiency, unevenness of support or difficult fabrication requirements. Such cavity modification has also not been applied to generalized plank stock for multiple use such as in packaging materials with lighter and more efficient closed cell foams.
There is, therefore, a need for a light weight cushion material with controlled range of force and motion and one which may obtain varied force properties along it's length to accommodate heterogeneously weighted bodies and comes "ready to use".
It is the object of this invention to provide such a cushion or stock material which may obtain a range of short, elongated or constant force curves, limited surface effects and a controlled range of motion and forces along it's length. It is a further object of this invention to produce a cushion material of lighter weight, orthopedic quality including both support and ventability and one which requires minimal assembly or cutting after initial production. It is also an object of this invention to provide a structure for producing flatter constant force curves which can be formed from any number of foams, elastomers, plastics or spring steel and, in particular, very lightweight and water proof closed-cell foam. Finally it is an object of this invention to introduce a general extruded closed-cell-foam cardboard stock material and several general uses for such.